Blinker Documentation¶
Blinker provides fast & simple object-to-object and broadcast signaling for Python objects.
The core of Blinker is quite small but provides powerful features:
a global registry of named signals
anonymous signals
custom name registries
permanently or temporarily connected receivers
automatically disconnected receivers via weak referencing
sending arbitrary data payloads
collecting return values from signal receivers
thread safety
Blinker was written by Jason Kirtand and is provided under the MIT License. The library supports Python 2.4 or later; Python 3.0 or later; or Jython 2.5 or later; or PyPy 1.6 or later.
Decoupling With Named Signals¶
Named signals are created with signal()
:
Every call to signal('name')
returns the same signal object,
allowing unconnected parts of code (different modules, plugins,
anything) to all use the same signal without requiring any code
sharing or special imports.
Subscribing to Signals¶
Signal.connect()
registers a function to be invoked each time
the signal is emitted. Connected functions are always passed the
object that caused the signal to be emitted.
Emitting Signals¶
Code producing events of interest can Signal.send()
notifications to all connected receivers.
Below, a simple Processor
class emits a ready
signal when it’s
about to process something, and complete
when it is done. It
passes self
to the send()
method, signifying that
that particular instance was responsible for emitting the signal.
Notice the complete
signal in go()
? No receivers have
connected to complete
yet, and that’s a-ok. Calling
send()
on a signal with no receivers will result in no
notifications being sent, and these no-op sends are optimized to be as
inexpensive as possible.
Subscribing to Specific Senders¶
The default connection to a signal invokes the receiver function when
any sender emits it. The Signal.connect()
function accepts an
optional argument to restrict the subscription to one specific sending
object:
This function has been subscribed to ready
but only when sent by
processor_b
:
Sending and Receiving Data Through Signals¶
Additional keyword arguments can be passed to send()
.
These will in turn be passed to the connected functions:
The return value of send()
collects the return values of
each connected function as a list of (receiver function
, return
value
) pairs:
Anonymous Signals¶
Signals need not be named. The Signal
constructor creates a
unique signal each time it is invoked. For example, an alternative
implementation of the Processor from above might provide the
processing signals as class attributes:
connect
as a Decorator¶
You may have noticed the return value of connect()
in
the console output in the sections above. This allows connect
to
be used as a decorator on functions:
While convenient, this form unfortunately does not allow the
sender
or weak
arguments to be customized for the connected
function. For this, connect_via()
can be used:
Optimizing Signal Sending¶
Signals are optimized to send very quickly, whether receivers are
connected or not. If the keyword data to be sent with a signal is
expensive to compute, it can be more efficient to check to see if any
receivers are connected first by testing the receivers
property:
Checking for a receiver listening for a particular sender is also possible:
Documenting Signals¶
Both named and anonymous signals can be passed a doc
argument at
construction to set the pydoc help text for the signal. This
documentation will be picked up by most documentation generators (such
as sphinx) and is nice for documenting any additional data parameters
that will be sent down with the signal.
See the documentation of the receiver_connected
built-in signal
for an example.
Blinker Changelog¶
Version 1.4¶
Released July 23, 2015
Verified Python 3.4 support (no changes needed)
Additional bookkeeping cleanup for non-ANY connections at disconnect time.
Added Signal._cleanup_bookeeping() to prune stale bookkeeping on demand
Version 1.3¶
Released July 3, 2013
The global signal stash behind blinker.signal() is now backed by a regular name-to-Signal dictionary. Previously, weak references were held in the mapping and ephermal usage in code like
signal('foo').connect(...)
could have surprising program behavior depending on import order of modules.blinker.Namespace is now built on a regular dict. Use blinker.WeakNamespace for the older, weak-referencing behavior.
Signal.connect(‘text-sender’) uses an alterate hashing strategy to avoid sharp edges in text identity.
Version 1.2¶
Released October 26, 2011
Added Signal.receiver_connected and Signal.receiver_disconnected per-Signal signals.
Deprecated the global ‘receiver_connected’ signal.
Verified Python 3.2 support (no changes needed!)
Version 1.1¶
Released July 21, 2010
Added
@signal.connect_via(sender)
decoratorAdded
signal.connected_to
shorthand name for thetemporarily_connected_to
context manager.
Version 0.9¶
Released February 26, 2010
Added
Signal.temporarily_connected_to
context managerDocs! Sphinx docs, project web site.
Version 0.8¶
Released February 14, 2010
Initial release
Extracted from flatland.util.signals
Added Python 2.4 compatibility
Added nearly functional Python 3.1 compatibility (everything except connecting to instance methods seems to work.)